Rifle scopes are provided with crosshairs or other reticle designs to provide an indication of an aiming point, where a bullet is expected to impact. Because bullets follow the path of an arc, the point of impact varies based on distance. Therefore, rifle scopes are normally equipped with adjustment knobs to shift optical components within the rifle scope to compensate for bullet drop. If a target distance is known, a knob adjustment is made based upon the predicted trajectory of the bullet. For a given type of ammunition, and elevation adjustment knob may be marked with distance markings to indicate to the shooter the proper setting for targeted a given distance. This is referred to as a “bullet drop compensator” (BDC).
A rifle scope elevation knob will typically have a detent mechanism that provides the shooter with tactile feedback of the number of “clicks” by which the knob has been rotated. Each click is a selected incremental angle of adjustment, and the clicks are all of the same value. Without a bullet drop compensator, a shooter must memorize or carry information indicating the number of clicks of adjustment required for a given distance.
Even with a bullet drop compensator, in dark conditions the shooter must rely on the tactile perception of the number of clicks, because bullet drop compensator markings may not be visible.
An adjustment knob with more clicks per degree or minute of angle will provide finer control, which is especially useful at greater distances. A coarser detent arrangement will provide less precision, but makes it easier for the shooter to count the number of clicks. For a distant target requiring a substantial adjustment to compensate for significant bullet drop, the shooter may be required to accurately count dozens of clicks. This slows the adjustment process, and is prone to errors that can be critical. Such errors can accumulate as the shooter makes further adjustments, such as to engage different targets, or to fine tune shot placement based on initial results.
The present invention overcomes the limitations of the prior art by providing a rifle scope having a body with a number of optical elements. An adjustment knob is rotatably connected to the body and interacts with at least one of the optical elements to provide an image shift in response to rotation of the knob. A detent mechanism interacts with the knob, and has a number of detent positions. Many of the detent positions have a first detent force, and a selected subset the detent positions have a greater second force. The selected subset of detent positions may correspond to selected major distance intervals.